Who is listed in the Participants list in the sidebar?

The list of Participants contains the person who added the message, plus all the persons that put the existing comments for that message.

If someone deletes all the comments that she/he added to that message, she/he will no longer appear in the list of participants.

How can I add emoticons to a message?

When editing a message you may choose an emoticon from the list that appears after you click on the small icon in the upper right corner of the message body text area.

Can I attach documents to a message?

Documents may be attached to a message and they will also appear in the list of files for that project, but as read-only.

When editing a message, the files attached to it may be replaced or deleted, based on the selection you make. Every file that you uncheck will be deleted upon save.

Can I attach an already uploaded file to a message?

Nope, this functionality is not yet present in Teamness. You may, however, delete the file from the file list and upload it again as part of a message.

Some files have the text "Attached to message" in the footer. What does it mean?

When you add or edit a message, you may also attach files to that message. These documents show up on the Files page as well, but since they are tied to a message, they cannot be edited in the files page.

You may remove a file attached to a message by editing that message and deleting it from there.

How can I see the list with all the tasks and messages assigned to a milestone?

For every task or message which is assigned to a milestone there is a link in the footer with the milestone's name, which will take you directly to the View milestone page. Also, for every milestone that has items assigned, there is a link in the footer of the milestone with the number of assigned tasks and messages.